1. Field of the Invention
The present invention relates to a mold for tire vulcanization and to a manufacturing method thereof, particularly to a mold for tire vulcanization by which a tire having excellent appearance can be obtained and production of defective tires during vulcanization can be decreased.
2. Description of the Prior Art
As a conventional mold for tire vulcanization, as shown in FIG. 4 of the accompanying drawings, a so-called insert segment type mold is well known, where a plurality of pieces 8 having an uneven interior corresponding to the land portions and the groove portions of at least the tread portion of a tire product are arranged adjacent each other and are disposed on a block 3 as a supporting means to comprise one segment 2. Furthermore the segments 2 are arranged adjacent each other, in other words are joined as a ring to form a predetermined interior configuration, as shown in FIG. 3.
In the case of the conventional mold of insert segment type where, as shown in FIG. 4, a plurality of pieces 8 are disposed on a block 3 as a supporting means to comprise one segment 2 and the segments are joined as a ring, it is necessary that an unvulcanized tire is pressed to the interior of the mold and is fitted thereto by inflation of a bladder. Therefore, air between the outer surface of the unvulcanized tire and the interior of the mold is exhausted through boundary portions 7 between adjacent pieces 8.
For such exhausting of the air between the tire and the mold, the boundary portion 7 between pieces 8 adjacent each other should be determined at the position where air remains during tire vulcanization and therefore a light spot bare tends to be generated. The term "light spot bare" refers to an incompletely molded portion on a vulcanized tire surface caused by air or water between the unvulcanized tire and the mold. However, setting the boundary portions at all positions where light spot bare tends to be generated causes an increase of the cost of the mold because of the increase of the number of the pieces or difficulty of manufacturing a piece.
The object of the present invention is to provide an insert segment type mold for tire vulcanization by which a tire having excellent appearance can be obtained and production of defective tires during vulcanization can be decreased, and to provide a manufacturing method thereof, without increase of the number of the mold pieces and increase of the cost because of complication of the boundary line configuration between the pieces.